著者

津村 建四朗

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.20, no.1, pp.30-40, 1967-06-25 (Released:2010-03-11)

参考文献数

3

被引用文献数

3 4

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Empirical formulas for the determination of the earthquake magnitude M from the duration of oscillation F-P have been derived from the observational data obtained by the Wakayama Micro-earthquake Observatory, Earthquake Research Institute.The instruments used by the Observatory and its substations are the short period vertical seismographs of the same characteristics (T1=1.0sec, T2=0.025sec, velocity sensibility=40-120uμ kine/mm at 1 to 10c/s).The formula obtained from the comparison of the F-P (sec) observed by the network with the M determined by the Japan Meteorological Agency is:M=-2.53+2.85log(F-P)+0.0014Δwhere Δ is the epicentral distance in km. This formula is applicable to the earthquakes with Δ<1000km and focal depth ≤60km.Since the coethclent for Δ is very small, the correction term of Δ can be neglected for the earthquakes with Δ<200km, and in this case the following simpler formula is more conveniently applied:M=-2.36+2.85log(F-P).The magnitudes obtained by the former and the latter formulas are designated, in the figures and table, MF-P and M′F-P respectively.The largest merits of this method are:1) Wide range of magnitude can be covered with a single seismograph, since there is no difficulty in reading F-P such as ‘saturation’ or ‘under exposure’ in the case of maximum amplitude.2) The treatment is very simple, especially for the earthquakes of short epicentral distances.